Are Pyrethroid Insecticides in Our Streams?

USGS scientist lifting a filter caked with sediment that's on top of a filter plate used for filtering suspended sediment from water samples. The filter was saved for later analysis for pyrethroid insecticides in the sediment. USGS scientists have developed a method to determine the concentration of a suite of pyrethroid insecticides absorbed to sediment particles. (Larger Version)

Transport in Water

A recent article in the Journal of Agricultural and Food Chemistry described how USGS scientists measured pyrethroids in water samples collected from urban streams and drains in the greater Sacramento area in California. The water samples were split into two phases, the dissolved (dissolved in water) phase and the particulate (associated with suspended sediments) phase. The amount of pyrethroids detected that were associated with the suspended sediments (particulates) ranged from 68 to 98 percent, even though the suspended sediment concentrations were relatively low (20 to 72 milligrams per liter (mg/L)). Measuring the occurrence and distribution of pyrethroids in these environmental compartments provides clues to understanding their fate. Whether the pyrethroids are in the dissolved phase or associated with suspended sediments influences their transport, persistence, bioaccumulation, and toxicity. Pyrethroids that are dissolved move through the water column and degrade differently from those associated with particulates. Fewer of the water samples are expected to indicate toxicity to aquatic organisms if only the dissolved water concentration was tested rather than the whole water concentration (the sum of both phases—water and sediment). Measuring pyrethroid concentrations in each phase, rather than as whole water (both phases combined) or in just one phase, allows for greater characterization and understanding of pyrethroids in the environment.